It is well known in the an that most living organisms cannot survive when exposed to certain wavelengths of intense light (e.g., ultraviolet wavelengths of about 250-260 nm) for a period of time. Small living organisms such as microbes generally cannot survive even short periods of intense ultraviolet (UV) irradiation. For this reason, UV light is frequently used for sterilizing or decontaminating equipment and products in both industrial and laboratory settings. For example, pharmaceutical companies often use UV light to sterilize objects before they are brought into a clean room environment where the pharmaceutical products are tested and manufactured.
In one particular use, UV light is used to sterilize or decontaminate items moving from a non-sterile environment, e.g. a normal atmospheric environment, to a "clean", i.e. decontaminated or sterile, environment. In so doing, it is important that the items being transferred not contaminate the clean environment, such as by beating viable organisms or other such contaminants from the non-sterile area into the clean area on the surface of a container holding sterilized products.
In this application, the item being transferred to a clean area is passed through a UV sterilization chamber, referred to as a ultraviolet passthrough, or UVP, sterilizer. Such UVP's generally have a door or the like in a non-sterile environment, a door in the clean environment, and a number of ultraviolet lamps. Only one of the two doors should generally be open at any given time to prevent the free flow of air-borne contaminants into the clean environment. The UV lamps are generally low-pressure mercury vapor lamps, which tend to have optimal emission distributions, with relatively intense emission in the range of about 253.7 nm.
In using such a UVP device to decontaminate, for example, the exterior surface of a container, an outer door in a non-sterile environment is opened and the container is placed inside the ultraviolet sterilizer, e.g. on top of a rigid support. The outer door is closed and the container is irradiated with ultraviolet light of a desired wavelength for a sufficient time to decontaminate the irradiated surface to the desired degree; an exposure time of about 30 seconds to about 3 minutes to radiation of about 2000-6000 microwatts per square centimeter at a wavelength of about 253.7 nm is usually sufficient to substantially sterilize a surface. The inner door, which opens to a sterile or "clean" environment, is opened after the sterilization cycle is finished and the sterilized container is removed through the inner door into the sterile environment.
One problem of current UVP systems is that they frequently do not irradiate the entire surface area of a container or other item in a single sterilizing cycle. Most such systems provide a rigid framework, e.g. a stiff metal mesh or screen, for supporting items to be sterilized within the UVP. Unfortunately, such supports tend to shield certain portions of the container from the ultraviolet light source, limiting effective sterilization of these surfaces.
Another problem presented by current UVP's is that the mercury vapor lamps can break. If such lamps do break, there is a significant risk of mercury contamination of not only the sterilizer, but also both the non-sterile and sterile environments. If mercury does escape, the entire operation of the contaminated clean room must usually be suspended until the mercury contamination is removed and the room can be returned to its "clean" standards. Mercury contamination can be especially troublesome in the pharmaceutical and medical industries because maximum permissible mercury levels in the clean areas are frequently very low. It is rather difficult and very time consuming to completely remove mercury contamination, so a broken mercury vapor lamp can be a rather expensive problem.